1. Field of the Invention
The present invention relates to a green-emitting phosphor composition and a cathode ray tube (CRT) manufactured using the same, and more particularly, to a green-emitting phosphor composition having improved luminance characteristics, degradation characteristics and afterglow characteristics, and a CRT adopting the same.
2. Description of the Related Art
Recently, with the advent of HDTV (high definition television) broadcasting, demands for projection type CRTs which can attain 40-inch or larger screens have been increasing for both home and business purposes. In the case of a projection type CRT, the fluorescent screen of a projection type CRT requires a brightness of several to several tens of times that of a direct viewing type CRT because an image is projected onto 40-inch, 52-inch or lager screens. Thus, the fluorescent screen of a projection type CRT should be excited under the condition in which a high-density current of several to several tens of times that of a direct viewing type CRT is applied. However, this results in deterioration of luminance, which is particularly serious in green-emitting phosphors which contribute to about 70% of the luminance.
As components of the conventional green-emitting phosphor, Y3Al5O12:Tb, Y3(Al, Ga)5O12:Tb, LaOCl:Tb, Zn2SiO4:Mn, InBO3:Tb or Y2SiO5:Tb, which have improved characteristics compared to Y2O2S:Tb, Gd2O2S:Tb or ZnS:Cu, Al, are used alone. However, these single-substance green-emitting phosphors do not fulfil all characteristics required for a projection type CRT. Thus, mixed green-emitting phosphors obtained by mixing Zn2SiO4:Mn or InBO3:Tb with Y3(Al, Ga)5O12:Tb, Y2SiO5:Tb or pigment-attached Y3(Al, Ga)5O12:Tb in an appropriate mixture ratio are put into practical use.
For example, Japanese Patent Laid-Open Publication No. hei 4-161483 describes a mixed green-emitting phosphor obtained by mixing Zn2SiO4:Mn with Y3(Al, Ga)5O12:Tb in order to improve color purity. Also, U.S. Pat. No. 4,559,469 describes a mixed green-emitting phosphor obtained by mixing Zn2SiO4:Mn with Y2SiO5:Tb in order to improve color purity.
However, the Zn2SiO4:Mn phosphor used for improving color purity in the mixed green-emitting phosphor for a projection type CRT, has poor degradation characteristic under the condition in which a high-density current is applied, while exhibiting excellent color purity. Thus, a decrease in the luminance is large with the passing of time. Also, due to a long afterglow time, the amount of the Zn2SiO4:Mn phosphor mixed with another phosphors is restricted. To avoid such a problem, there has been an attempt to improve luminance and afterglow characteristics by mixing a fluoride compound instead of the Zn2SiO4:Mn phosphor, as disclosed in U.S. Pat. No. 4,336,313.
Conclusively, the Zn2SiO4:Mn phosphor mixed for improving color purity in the mixed green-emitting phosphor for a projection type CRT has a very long afterglow time, that is, about 30 ms, and has poor luminance and degradation characteristics. Thus, as the amount of the mixed Zn2SiO4:Mn phosphor increases, luminance and degradation characteristics of the mixed green-emitting phosphor become poorer.
To solve the above problems, it is an object of the present invention to provide a new green-emitting phosphor composition which can replace a conventional green-emitting phosphor composition containing a Zn2SiO4:Mn phosphor.
It is another object of the present invention to provide a cathode ray tube (CRT) manufacturing using the new green-emitting phosphor composition.
Accordingly, to achieve the first object, there is provided a green-emitting phosphor composition comprising:75 to 95 wt % of a phosphor of the formula Y2SiO5-Tb, and 5 to 25 wt % of a phosphor of the formula SrGa2S4:Eu.
Preferably, the phosphor of the formula Y2SiO5:Tb contained in the composition is 85 to 95 wt %, and the phosphor of the formula SrGa2S4:Eu contained in the composition is 10 to 15 wt %.
To achieve the second object, there is provided a cathode ray tube manufacturing using the green-emitting phosphor composition.